A method and an apparatus for bio-electrochemical denitrification of fluids in which electric power may be harvested are known from WO 2011/006939 A2. In the known method, a preliminary sedimentation takes place in an anode cell in which an anode is arranged for bio-electrochemically converting carbon-containing compounds. Next, carbon is removed and a nitrification occurs in an aerobic reactor. A final sedimentation takes place in a cathode cell including a cathode for bio-electrochemical denitrification. In the aerobic reactor, a method of fluid clarification with sessile biofilms is executed. The anode cell and the cathode cell are spatially separated and not connected via a membrane; the fluid flows through the cells and the aerobic reactor continuously or in batches. Electrons are transported from the anode to the cathode via an electrical conductor, and protons are transported via the flow of the fluid. The proton or ion transport may further take place via a salt bridge provided between the anode cell and the cathode cell.
The conditions for harvesting relevant amounts of electric energy in the method and the apparatus known from WO 2011/006939 A2 are not good. Due to the spatial distance of the anode to the cathode and the correspondingly long electrical conductor connecting them, and due to the proton or ion transport via the flow of the medium or via the salt bridge, the electric internal resistance is very high, particularly when compared to the low voltage dropping between the anode and the cathode of typically less than 300 mV.
A method and an apparatus for bio-electrically producing hydrogen from organic ingredients is known from WO 2009/008709 A1. Here, an anode chamber in which an anode is arranged is separated from an cathode chamber in which a cathode is arranged by means of an ion-selective membrane permeable for protons. A biofilm is grown on the anode. During this growth, an external voltage is applied between the anode and the cathode. The fluid with the organic ingredients is acidified before it is supplied to the anode. The overall conditions are set such that the biofilm produces hydrogen.
Methods and apparatuses for generating electric energy from flowing waste water with organic ingredients are also known from US 2010/0304226 A1, US 2014/0030555 A1, and US 2012/0132521 A1.
U.S. Pat. No. 3,340,094 A discloses a method of directly producing electrical energy through the biochemical reaction of photosynthetic bacteria. This production of electrical energy takes place in a fuel cell whose anode and cathode can be connected to an alternator for conversion of the low voltage direct current produced by the fuel cell into alternating current whose voltage can be stepped up by a transformer.
There still is a need of a method and an apparatus for bio-electrically generating electric power from organic ingredients of a waste water at least intermittently flowing in a flow direction, which allows for an effective generation of electric power particularly in the processing of industrial and municipal waste waters in existing waste water treatment plants.